An improved non-dimensional model of wet-cooling towers

Abstract: A general non-dimensional mathematical model of cooling towers is improved by including evaporation of water. The solution still consists of adjusting the assumed straight air-saturation line to the real air-saturation data, but a new constant (H) is added as well. Two solutions are proposed and the accuracy of each method is checked against data from the literature and also compared with the original solution. The first method shows a maximum decrease of 4.4 per cent in error, whereas in the second method, the maximum error was found to be 3.3 and 6.8 per cent when the inlet air was unsaturated and saturated, respectively. Keywords: cooling tower, non-dimensional model, evaporatio

Prediction of evaporation losses in wet cooling towers

The accurate prediction of all aspects of cooling tower behavior is very important. Accurately predicting evaporation losses is significant because water in cooling towers is cooled primarily through the evaporation of a portion of the circulating water, which causes the concentration of dissolved solids and other impurities to increase. An empirical relation is developed on the basis of ASHRAE’s rule of thumb that is simple and accurate with a wide range of applicability. The predicted values are in good agreement with experimental data as well as predictions made by an accurate mathematical model

Second-law-based performance evaluation of cooling towers and evaporative heat exchangers

Abstract In this paper, we present thermodynamic analysis of counter flow wet cooling towers and evaporative heat exchangers using both the first and second laws of thermodynamics. A parametric study is carried out to determine the variation of second-law efficiency as well as exergy destruction as a function of various input parameters such as inlet wet bulb temperature. Irreversible losses are determined by applying an exergy balance on each of the systems investigated. In this regard, an engineering equation solver (EES) program, with built-in functions for most thermodynamic and transport properties, is used. The concept of total exergy as the sum of thermomechanical and chemical parts is employed in calculating the flow exergies for air and water vapor mixtures. For the different input variables investigated, efficiencies were, almost always, seen to increase or decrease monotonically. We notice that an increase in the inlet wet bulb temperature invariably increases the second-law efficiency of all the heat exchangers. Also, it is shown that Bejan’s definition of second-law efficiency is not limited in evaluating performance. Furthermore, it is understood that the variation in the dead state does not significantly affect the overall efficiency of the system. © 2006 Elsevier Masson SAS. All rights reserved. Keywords: Exergy; Evaporative cooler; Evaporative condenser; Dead stat

A complete model of wet cooling towers with fouling in fills

Abstract A cooling tower basically consists of three zones; namely, spray zone, packing and rain zones. In cooling towers, a significant portion of the total heat rejected may occur in the spray and rain zones. These zones are modeled and solved simultaneously using engineering equation solver (EES) software. The developed models of these zones are validated against experimental data. For the case study under consideration, the error in calculation of the tower volume is 6.5% when the spray and rain zones are neglected. This error is reduced to 3.15% and 2.65% as the spray and rain zones are incorporated in the model, respectively. Furthermore, fouling in cooling tower fills as well as its modeling strategy is explained and incorporated in the cooling tower model to study performance evaluation problems. The fouling model is presented in terms of normalized fill performance index (gF,norm) as a function of weight gain due to fouling. It is demonstrated that the model is asymptotic, which is similar to typical asymptotic fouling model used in conventional heat exchangers. � 2006 Elsevier Ltd. All rights reserved. Keywords: Cooling tower; Spray zone; Rain zone

An improved non-dimensional model of wet-cooling towers

Abstract: A general non-dimensional mathematical model of cooling towers is improved by including evaporation of water. The solution still consists of adjusting the assumed straight air-saturation line to the real air-saturation data, but a new constant (H) is added as well. Two solutions are proposed and the accuracy of each method is checked against data from the literature and also compared with the original solution. The first method shows a maximum decrease of 4.4 per cent in error, whereas in the second method, the maximum error was found to be 3.3 and 6.8 per cent when the inlet air was unsaturated and saturated, respectively. Keywords: cooling tower, non-dimensional model, evaporatio